State Rep. Ed Sullivan Jr. said he will support a bill to allow gay marriage in Illinois, becoming the second House Republican to do so and first among leadership.

State Rep. Ed Sullivan Jr. of Mundelein said Sunday he will support a bill to allow gay marriage in Illinois, becoming the second House Republican to do so and first among leadership.

Sullivan, who is chairman of the House Republican campaign organization, said his decision to back same-sex marriage represented a personal and family evolution on the issue. Previously an opponent of civil unions, Sullivan told the Tribune that his mother-in-law, who lives in the southwest suburbs, has been in a same-sex relationship.

"The first reaction from people might be, 'Well he might be voting for that just because of his mother-in-law,'" Sullivan said. "The reality is, because my mother-in-law is gay, I have more of an understanding and familiarity with same-sex couples."

A state representative since 2003, Sullivan and state Rep. Ron Sandack of Downers Grove are the only House Republicans to publicly announce their backing of the same-sex marriage bill, which already passed the state Senate. With House lawmakers returning to Springfield on Monday after a two-week break, supporters of the measure have said they were within a dozen votes of the 60 needed to pass it.

Sullivan said he believes more Republicans among the 47 in the House will sign on.

"There is tremendous momentum leading up to this vote. I think we're very close," he said. "There's many of my colleagues that have talked about this, that have said it's the right thing to do."

Same-sex marriage has been controversial for Republicans in the state. Illinois GOP Chairman Pat Brady urged lawmakers to pass the bill, but some social conservatives unsuccessfully sought his ouster because his position conflicted with a plank in the state Republican platform opposing same-sex marriage.

Recently, U.S. Sen. Mark Kirk, a Brady supporter, announced his support for gay marriage, becoming the second U.S. Senate Republican to do so.

"This issue for me ... goes to the core of fairness -- marriage equality for all people. I think it is in line with ... what I believe, and I personally believe it is in line with what our party believes, and that's trying to treat people with fairness," Sullivan said.

Sullivan said he believes his decision follows the wishes of voters in his northwest suburban district. He acknowledged that opponents cite their religious beliefs but said the bill contains strong religious protections.

"I try to err on the side of being a public servant and serving my district as opposed to potentially being a politician and just serving that subset (opposed based on religion) and those within my party who don't necessarily want this to pass," he said. "I look at this as a freedom, as a conservative view of treating people equally."